The extracellular matrix glycoproteins laminin and entactin are synthesized and secreted by a variety of cells. They appear to be essential components of many types of basement membranes and mediate the attachment of cells to the extracellular matrix. The objectives of this research are: (1)\to attempt to elucidate the structures of the region of the glycoproteins responsible for cell adhesion; (2)\to obtain information on the receptor sites on the plasma membranes that bind the glycoproteins; and (3)\to explore the specificity of interaction between the glycoproteins and receptors from different sources. An extracellular matrix-coated bead that consists predominantly of laminin and entactin in a naturally occurring complex has been developed. The attachment and spreading of human mammary tumor MCF-7 tumor cells, African Green Monkey BSC cells, and a variety of other cells are differentially affected by the matrix. Hybridomas have been developed from immunized rat spleen cells fused to mouse myeloma cells that secrete monoclonal antibodies against the GP-2 subunit of laminin. These monoclonal antibodies are being used to define the organization of laminin in the basement membranes of developing and adult mouse tissues and human tissues. These reagents have revealed that laminin is organized in topographically distinct ways in basement membranes during development and even in different regions of a single organ. The developments mentioned above represent efforts to attain the long-range objectives of this project to understand the subtle interactions between cells and their underlying matrix in metastasis, embryogenesis, and cell differentiation. (A)